HP3468A repair

[alessandro93]

Hi, this is my first post on the eevblog forum 

I'm trying to repair an HP3468A multimeter.
All the voltages are OK, when I switch it on the display remains blank but I can hear some relays clicking  (sometime every second, sometime with a 2 seconds pause after 2 clicks )

On the back of the LCD there are 2 COBs one of which seems to have a bulge and a small hole in it. Maybe it blew up but If I disconnect the LCD connector, then reconnect it but not all the way in and I start to wiggle it sometimes appear something.  I made a video on this here: https://youtu.be/W3ywXtQ3IkY from minute 0:18

Reading the troubleshooting guide I should use a signature analyzer but of course I haven't got one and I guess I can't use a rigol ds1054z for this, right?

The PCB is quite oxidized, probably due to heavy humidity and the HP-IL chip U503 pins ar quite corroded

Finally probing the EPROM U502 and other chips (the CPU also)  seems to have a lot of garbage on their signals, look the screenshots.


What do you think?

Thanks.

[Ordinaryman1971]

I can't see the video, it says the owner disabled it.
Did you make any progress fixing it?
I wonder, I have the same meter kind of meter with a problem as well.
I can't see the video of yours so it's hard for me to say if it's the same kind of problem. I will take some pictures tomorrow and post them.
Not sure if somebody would have a suggestion where to start troubleshooting.
When turned on the meter hangs on the self test. The screens blinks every second and displaying all the characters... that's it.
I should probably start reading service manual but.. .it's late, maybe somebody have done it already.
So far I've checked the battery it's 3V, I guess it's still good.
Well... need to post pictures.

[alessandro93]

Hi, thanks for your reply.
Now the video should be visible.
I didn't make any progess unfortunately, ayway my problem is slightly different, the LCD remains always blank

[frantisek]

Display KO .

[Le_Bassiste]

Hi, thanks for your reply.
Now the video should be visible.
I didn't make any progess unfortunately, ayway my problem is slightly different, the LCD remains always blank

as per your video, i'd suggest that the LCD is at least partially intact. don't know what you did on the displays back during video, probably wiggling the ribbon connector. as you are already estimating the LCD to be at the point of write-off,  try these two final desperate steps (no guarantee against burnt pancakes, though!):
1) use a flat watchmaker's screwdriver, a butter knife or something similar flat and blunt and try to lift off the ribbon cable connector from the display. do that evenly on both sides of the connector. do not "tilt" the connector while lifting it. the contact prongs are extremely delicate and fragile. inspect the contacts and give them a thorough cleaning to remove all corrosion (if there is any) this is the less severe surgery.

2) now for the severe surgery: peel away the two u-shaped metal beams from upper and lower rim of the display. now you can carefully lift off the LCD glass and inspect the two zebra connectors that contact the LCD to the pcb. wear gloves. a single fingerprint may ruin the contact surfaces of the zebras, and there is no way to clean them after such an accident.  however, from the video, this step shouldn't be necessary. so you better don't do this. 

as for the HPIL chip: looks like somebody has been in there before and did one hell of a job to re-solder the chip in place. seems that guy used some solder for roof-tinning...

good luck and keep us posted!